Definition of Clemmensen Reduction

Clemmensen reduction is a reaction in which the aldehydes and ketones are reduced (deoxygenated) to a corresponding hydrocarbon. This reaction takes place in the presence of zinc/mercury alloy which is also known as zinc amalgam. In the first step of the reaction, the aldehyde or ketone is heated in the presence of finely divided Zn/Hg amalgam and hydrochloric acid.


The mercury present in amalgam serves the purpose of providing a clean active metal surface. The substrate used in this reaction should be stable in a strongly acidic environment. This reaction is complementary to the Wolff Kishner reaction which takes place in the presence of a strong alkali.

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